MYP Agar (Mannitol Yolk Polymyxin Agar)
MYP Agar (Mannitol Yolk Polymyxin Agar)
ISO 7932 Reference Medium for Bacillus cereus Enumeration
Catalog Number: AS-1303
Overview
MYP Agar (Mannitol Yolk Polymyxin Agar), also known as Bacillus cereus Agar, is the international gold-standard selective and differential solid medium for the isolation and enumeration of the Bacillus cereus group from food and environmental samples. The medium is the official reference medium specified in ISO 7932 (current revision) and is also described in FDA-BAM Chapter 14 and other major food microbiology standards.
MYP Agar enables reliable differentiation of presumptive B. cereus colonies based on mannitol non-fermentation and lecithinase activity, producing a distinctive colony morphology.
Applications
• Enumeration of presumptive Bacillus cereus in foods such as spices, cereals, dairy, meat, and ready-to-eat meals
• Official reference medium for ISO 7932, FDA-BAM, and USDA-FSIS methods
• Detection of emetic and diarrhoeal toxin-producing B. cereus strains
• Food safety monitoring and environmental hygiene testing
Key Features & Benefits
• Mannitol non-fermentation keeps B. cereus colonies red-pink
• Egg-yolk emulsion reveals strong lecithinase (phospholipase C) activity
• Polymyxin B suppresses Gram-negative bacteria and most competing flora
• Characteristic “fried-egg” colony appearance enables easy presumptive identification
• Recognised international reference medium for food microbiology
Principle of the Medium
Mannitol is not fermented by Bacillus cereus, so colonies retain a red-pink colour in the presence of phenol red. Lecithinase activity on egg-yolk emulsion produces a dense opaque white precipitation zone surrounding colonies. Polymyxin B selectively inhibits Gram-negative organisms and many Gram-positive contaminants, allowing selective recovery of the B. cereus group on a nutritionally supportive base.
Typical Composition (per litre)
Meat Extract / Beef Extract – 1.0 g
Peptone – 10.0 g
D-Mannitol – 10.0 g
Sodium Chloride – 10.0 g
Phenol Red – 0.025 g
Agar – 15.0 g
Supplements (added after sterilisation)
Polymyxin B – 100,000 IU (approx. 25–30 mg)
Egg-yolk emulsion (50%) – 100 mL
Final pH: 7.2 ± 0.2 at 25 °C
(Composition may be adjusted to meet specific regulatory or published standards.)
Preparation
Suspend 46.025 g of dehydrated base in 900 mL purified water.
Heat with agitation and boil for 1 minute to dissolve completely.
Sterilise by autoclaving at 121 °C for 15 minutes.
Cool to 45–50 °C.
Aseptically add 100 mL sterile 50% egg-yolk emulsion and filter-sterilised polymyxin B supplement.
Mix gently (avoid air bubbles) and pour plates.
Incubation
Incubate at 30 ± 1 °C for 24–48 hours.
(Some laboratories incubate at 35–37 °C; both conditions are acceptable depending on protocol.)
Typical Colony Appearance (24–48 h)
Bacillus cereus group: 3–6 mm pink-red colonies, dry or crumbly, surrounded by a wide opaque white precipitation zone (lecithinase positive)
Other Bacillus spp.: usually smaller colonies with weak or absent precipitation
Most other organisms: inhibited
Confirmatory Tests (Required)
• Haemolysis on blood agar
• Motility
• Voges–Proskauer reaction
• Anaerobic glucose fermentation
• Nitrate reduction
Storage & Stability
Prepared plates: Store at 2–8 °C, sealed, and use within 2 weeks
(Egg-yolk emulsion is perishable and limits plate shelf life.)
Intended Use
For food microbiology and environmental testing use only.
Not for human, veterinary, pharmaceutical, or therapeutic use.
Quality & Compliance
Manufactured under controlled conditions for batch-to-batch consistency.
Meets performance expectations of ISO 7932 reference methodology.
Performance comparable to leading international food microbiology media suppliers.
Customs & Trade Information
HS / AHECC Code: 3821.00.00
Prepared culture media for the development or maintenance of microorganisms